This invention relates to disposable hypodermic ampoules having two chambers for mixing a powdered medicament with a diluent prior to injecting the mixed ingredients into a patient through a needle externally affixed to the ampoule.
A number of drug compounds, including some antibiotics, some vaccines, and several other injectable products, require that an active ingredient (usually in a powder form) be mixed with an injection vehicle or diluent (usually water) shortly before administration. One widely accepted procedure for mixing powder and liquid medicament components is to provide them in separate vials, each having its own rubber stopper closing its outlet opening. The liquid is withdrawn from its vial by a needle and syringe, and is then injected into the vial containing the powder. The thus-mixed liquid and powder in the latter vial, after shaking it where required, is withdrawn as a dispersion by the same needle and syringe, and the injection is effected therewith in a conventional manner.
Since this is a relatively cumbersome and time-consuming technique, and since it requires careful handling of the syringe during the mixing operation to maintain sterility of the needle prior to the injection, attempts have been made to provide an injection syringe which itself contains the powder and liquid medicaments in separate chambers which are arranged so that the powder and liquid medicaments may be mixed just prior to an injection. Those ampoules may be broadly classified into contained-needle type injection devices and external needle-type injection devices.
The contained-needle type injection device is shown and described in U.S. Pat. No. 3,735,761 to Hurschman et al. In that patent, there is disclosed a multichamber, hypodermic device which includes first and second coaxially disposed cylinders. The cylinders respectively provide first and second, medicament-containing chambers, the adjacent ends of which are separated by a first, puncturable, piston-like diaphragm. This first diaphragm extends across and around the end of the first cylinder to close and seal the same, and is slidably mounted in the adjacent end of the second cylinder to close and separately seal the same. The other end of the first cylinder slidably carries a plunger and a hypodermic needle is mounted on the plunger with its pointed end extending axially toward a pierceable, central portion of the first diaphragm. The other end of the second cylinder is closed and sealed by a puncturable diaphragm having its pierceable portion also axially aligned with the pointed end of the needle. A powder medicament in the first chamber and a liquid medicament in the second chamber are mixed by partially depressing the plunger so that the pointed end of the needle cannula pierces the first diaphragm. Liquid flows from the second chamber through the needle and into the first chamber as the first diaphragm moves toward and into engagement with the second diaphragm, thus mixing the two medicaments. An injection may be effected by further depressing the plunger to the end of its stroke while holding the ampoule against the skin of the patient.
While contained-needle type injection devices are suitable for many injection purposes, many physicians and nurses prefer to perform an injection with a more conventional syringe having an external needle which is manually inserted into the skin of the patient, since contained-needle type devices are primarily suited for use in a mechanical spring-actuated applicator. While the use of applicators has many advantages, it is impossible to express air from the ampoule prior to an injection and is impossible to aspirate the syringe during an injection to ensure that a blood vessel is not pierced by the needle. Also, applicators are not entirely suitable for veterinary use, since animals vary in size and coat.
In view of these problems, attempts have been made to provide two-chamber syringes having an external needle which are adapted to perform a standard injection after mixing the medicaments within the syringe. For example, U.S. Pat. No. 3,342,180 provides a vial which is separated into two chambers by a plunger. Powder is provided in a lower chamber and liquid is provided in the upper chamber. The plunger is provided with a one-way check valve so that upon retraction of the plunger, the liquid is forced through the valve and into the compartment containing the powder. The vial is provided with an external needle at its lower end so that the mixed medicament may be injected into the patient. This arrangement involves complicated valving in the separating plunger and therefore requires extremely complex plunger molding operations. A similar arrangement is shown in U.S. Pat. No. 3,330,280, wherein a plunger is provided with a displaceable plug to provide communication between the two chambers prior to injection. Other patents, such as U.S. Pat. No. 2,591,046, include complex passageways formed into the glass sidewall of the vial to provide communication between two chambers upon movement of an intermediate diaphragm. A major deficiency of prior art two-chamber devices is that, while they appear theoretically feasible, they are difficult, if not impossible, to assemble, fill, and/or freeze-dry with conventional equipment and know-how.
A more acceptable two-chamber syringe is set forth in U.S. Pat. No. 2,193,322. In that patent, the patentees provide a two-chamber injection device having an end diaphragm and an intermediate diaphragm which are sequentally pierced by one pointed end of a double-pointed needle to provide communication between the two chambers. Since the two chambers are illustrated as having fluid therein, the intermediate diaphragm is hydraulically locked against movement relative to the vial. Therefore, although the device according to that patent is suitable for mixing and then injecting two liquids, it is not suitable for mixing a liquid with a powder, since the intermediate diaphragm would not be hydraulically locked in position and would be moved by the piercing needle upon engagement. Furthermore, the device shown in that patent is not capable of having air expressed from the mixed medicament chamber prior to an injection, since air would be trapped between the opening at the end of the needle and the intermediate diaphragm upon plunger movement.